Hu, Huanzhi;
(2025)
Quantum Fluctuations in Kondo Materials and Kitaev Quantum Spin Liquids.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
In strongly correlated systems, quantum fluctuations play a crucial role in the ordering at low temperatures, leading to various exotic ground states. The critical points usually correspond to some universal scaling behaviours, which can be described phenomenologically by the Ginzburg-Landau-Wilson paradigm. However, it breaks down in systems where gapless fermionic excitations or topological features play a key role. Understanding such cases is crucial to explaining complex behaviors in quantum materials, such as unconventional magnetism and quantum spin liquids. This thesis focuses on some different scenarios where the presence of gapless fermions alters the behavior of the phase transitions. Firstly, we use the perturbative and numerical renormalisation group to study the role of Kondo fluctuations in an anisotropic Kondo model to explain the moment reorientation and hard-direction ordering in Kondo materials. Secondly, we study the antiferromagnetic quantum criticality when the local moments are Kondo-coupled to Dirac fermions, and show that the N´eel critical point is stable against the particle-hole fluctuations. In the last part, both the magnetic and topological phase transitions of the Kitaev-Ising model are studied and compared through different Majorana fermion representations, and then a renormalisation group approach is applied to the topological phase transition of the gapless and gapped quantum spin liquid states. It turns out that in the presence of other magnetic interactions, the topological phase transition can be studied in a similar manner as the symmetry-breaking phase transitions of semi-Dirac fermions. The results in this thesis contribute to the theoretical understanding of fermionic quantum criticality and the nature of novel quantum phase transitions in strongly correlated electron systems.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Quantum Fluctuations in Kondo Materials and Kitaev Quantum Spin Liquids |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy UCL |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10212108 |
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